Phase II trial of the anti-prostate specific membrane antigen (PSMA) monoclonal antibody (mAb) J591 plus low-dose interleukin-2 (IL-2) in patients (pts) with recurrent prostate cancer (PC)

Abstract

15558 Background: The de-immunized mAb J591 recognizes the extracellular domain of PSMA and was engineered to induce antibody-dependent cellular cytotoxicity (ADCC). Low-dose IL-2 results in the clonal expansion of NK cells and may enhance ADCC. We conducted a phase 2 trial to determine the efficacy and toxicity of mAb J591 plus low-dose subcutaneous (SC) IL-2 in pts with recurrent PC. Methods: 17 pts with recurrent PC (2 groups: 11 with PSA relapse only; and 6 with progressive castrate metastatic disease) received continuous low-dose SC IL-2 (1.2 x 106 IU/m2/day) daily for 8 weeks with mAb J591 (25 mg/m2 IV) weekly on weeks 4, 5 and 6 (1 cycle). Pts could receive a maximum of 3 cycles. Results: 16 evaluable pts received up to 3 cycles of therapy (16 pts, one cycle, 9 two cycles and 2 three cycles). Toxicity was mild and limited to fatigue and injection site reactions. At the end of cycle 1, PSA was stable (-50%<change in PSA<25%) in 9 of 16 patients, with PSA declines up to 34%. No PSA decline >50% was observed. A post-hoc analysis of PSA kinetics showed 5 patients had a reduction in their PSA slope of =25%; 8 of the remaining 11 patients demonstrated PSA stabilization (- 25%<change in PSA slope<25%). PSA response was most commonly observed during weeks 4–6 of the cycle correlating with mAb administration. Flow cytometric analysis of peripheral blood mononuclear cells revealed an average increase in absolute NK cell count of 107% at week 4 and 117% at the end of cycle 1. Conclusions: The combination of mAb J591 with low-dose IL-2 was well tolerated and inhibited PSA kinetics in some patients, however no responses were seen. Repetitive dosed mAb J591 is a viable strategy for use in combination with immune modulatory or other therapies in recurrent prostate cancer. No significant financial relationships to disclose.